1. Field of the Invention
This invention relates to an automatic exposure control device for a camera and, more particularly, to an automatic exposure control device for a diaphragm preference type single-lens reflex camera performing digital control.
2. Description of Prior Art
Generally, in a diaphragm preference type single-lens reflex camera that performs digital control, analog time information which is obtained as a result of analog computation made through light measurement and setting of photographing information is converted by analog-to-digital means into digital time information; this is digitally stored and expanded to real time in response to a shutter release action of the camera to obtain digital shutter time; and a shutter is controlled thereby.
Such digitalization of a camera makes possible the automation, reduction in size and enhancement of accuracy of the camera. However, in addition to the enhancement of accuracy, the cost of the camera must be lowered.
A camera of the above mentioned digital control type has been arranged to perform digital control with a second counter provided for sequence control over various parts of the camera and a first counter provided for carrying out analog-to-digital conversion for photometric computation.
Reduction in the number of steps of these counters greatly contributes to reduction in cost. Digitalized electronic cameras, in general, use a plurality of integrated circuits (ICs). The cost of the ICs lowers as the area of chips of ICs is made smaller. Accordingly, in order to lower the cost, the number of gates must be reduced even by one. Each step of the counter requires about 10 gates or thereabout. Reduction in the number of counter steps, therefore, greatly contributes to reduction in cost.
In a camera system, it is only a self-timer that requires a long period of time with the exception of unusually long time exposure. If a counter is to be separately arranged exclusively for timer control, the second counter must have many stages including about 20 steps just for a self-timer. This has been a great obstacle to cost reduction.